I admit that about 90% of this decision was based on my housemate and I watching the complete Lord of the Rings cycle (Hobbit films first) one film a night for a week. You can't expose yourself to that much high fantasy without wanting to paint elves, not when you're a Warhammer player.
And because I am a painfully indecisive person (who also has a small Wood Elves army already) it'll be an Army of the Eternity King (minus the Eternity King because I hate that model). I love all three of Warhammer's elven races: the High Elves in their white robes, the Dark Elves with their serrated blades and the Wood Elves with all the longbows you could ever want. There are so many specialist units I so want to paint: Executioners, Swordmasters, Eternal Guard and so forth. I think this project will be less building to a plan and more picking up whatever catches my fancy.
About the only definite idea I have for the army is that the general will be a Loremaster Of Hoeth.
Korando of Hoeth is an old character of mine, though this will be the first time I've used him as a general. He used to be a mercenary captain for games of Triumph & Treachery who led a small unit of Shadow Warriors. He's a wanderer and the army I'll be building represents less an official alliance than people he's picked up on the way.
Whatever else, this'll be a fun story to write and an interesting army to paint.